I think they should conquer/ open diplomacy with the three DLC locations, at least after strengthening their position. The Pitt would give plentiful ammo and weapons, and there would be a possibility of a cure for mutation. Point Lookout provides a cheap cure for radiation, but the locals may cause heavy losses. And Mothership Zeta can give extremely advanced tech, and a superlaser to intimidate enemies.

I thing they should play it cool, and build strenght, then send some men out to surrounding areas and get a feel for the inhabitants.

If they would like to be a part, the they should expant, but if they do not want to be apart they should be left alone. Unless they pose a threat of coarse.

They should head up north to New York and the institute